AbstractThe influence of the feeding regime on surfactant and nutrient removal and biomass production was evaluated in three high rate algal ponds for primary domestic wastewater treatment. Feeding times of 24, 12 and 0.1 h d−1 were studied in each reactor at a similar hydraulic retention time of 7.0 days and organic load of 2.3 mg m−2 d−1. Semi-continuous feeding at 12 and 0.1 h d−1 showed better microalgal biomass production (0.21–0.23 g L−1) and nutrient removal, including nitrogen (74–76%) and phosphorus (80–86%), when compared to biomass production (0.13 g L−1) and nitrogen (69%) and phosphorus (46%) removals obtained at continuous feeding (24 h d−1). Additionally, the removal efficiency of surfactant in the three reactors ranged between 90 and 97%, where the best result was obtained at 0.1 h d−1, resulting in surfactant concentrations in the treated effluent (0.3 mg L−1) below the maximum freshwater discharge limits.
The influence of CO2 addition and feeding regime (continuous versus semicontinuous) on the removal of Pseudomonas aeruginosa, Clostridium perfringens, Staphylococcus, Enterococcus faecalis, and Escherichia coli (E. coli) from three shaded high-rate algal ponds (HRAPs) treating raw sewage (RS) was studied. The three HRAPs were operated at an analogous hydraulic retention time (HRT) for 5 days and with shading of 50%. The CO2 addition and feeding regime had no statistically significant influence on the removal of Pseudomonas aeruginosa, Clostridium perfringens, Staphylococcus sp., and Enterococcus faecalis, with 2.39–3.01, 2.07–2.31, 3.02–3.38, and 3.14–3.45 log units, respectively. However, the removal of E. coli decreased significantly with the feeding regime of 0.1 h d−1 and 2.23–3.29 log units. The productivity and the total suspended solids (TSS) removal efficiency were significantly improved with the semicontinuous feeding regime and CO2 addition. The highest productivity was obtained in the semicontinuous feeding regime, 5.93 g m2 d−1, while the TSS removal efficiency was similar between the semicontinuous feeding regime and CO2 addition (31–36%). The control of light intensity led to greater variability in the algal community, and was present in the three reactors, in different proportions, in the form of the microalgae Scenedesmus acutus, Scenedesmus obliquus, and Chlorella sp.
Microalgae–bacteria systems are used for the treatment of effluents, using a technology that has stood out with excellent results, as reported in the literature. However, investigating these systems in more depth can improve our understanding of the removal mechanisms for a wide range of existing and emerging pollutants and help improve the guidelines for design and operation, in order to improve the treatment efficiency as well as biomass productivity. This work studied the impact of the feeding regime on the removal of metals and pathogens from primary domestic wastewater in high rate algal ponds (HRAPs). For this, one reactor was fed continuously (HRAP1) while two reactors were fed in semi-continuous mode, during 12 h day−1 (HRAP2) and 0.1 h day−1 (HRAP3). Although removal efficiencies of 82 ± 5% for Mn and 90% for E. coli were reached in the semi-continuously fed reactors, there was no significant difference between the conditions studied. On the other hand, for biomass productivity, the semi-continuous feeding regime was more advantageous with a growth of ≈ 22 mg L−1 day−1.
O trabalho teve a finalidade de avaliar quais tipos de cultivo e condições operacionais são mais eficientes na remoção de nutrientes do esgoto doméstico primário em sistemas de microalgas-bactérias. Para isso, diferentes condições experimentais foram estudadas utilizando como inóculo microalgas e/ou bactérias bem como o efeito da luz e a adição de gases (gás carbônico e ar atmosférico). As remoções foram mais expressivas nos fotobiorreatores inoculados com microalgas (com predominância de Chlorella vulgaris) e bactérias, em presença de luz. Além disso, as condições que receberam suplementação de gás (MB+CO2 e MB+O2) obtiveram remoções superiores às demais condições, em relação ao nitrogênio total (93 ± 0,2% e 95 ± 1,8%, respectivamente), carbono orgânico total (84 ± 0,2 e 86 ± 0,1%) e carbono inorgânico (95 ± 0,7 e 95 ± 0,3%). Por fim, foram também nestas condições que se obtiveram os melhores resultados de crescimento da biomassa, com produtividade máxima de 179 e 267 mgSST L-1 d-1.
Palavras-chave: Carbono. Chlorella vulgaris.Fósforo. Nitrogênio. Tratamento de efluentes.
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